In many subterranean environments, such as wellbore environments, downhole tools are used to carry out a variety of procedures. For example, downhole tools may comprise a variety of flow control valves, safety valves, flow controllers, packers, gas lift valves, sliding sleeves, and other well tools. Many of these well tools can be hydraulically controlled via input from hydraulic control lines that are run downhole. Conventional well tools often rely on a dedicated hydraulic control line or lines routed to a specific tool positioned in a wellbore. The number of well tools placed downhole can be limited by the number of control lines available in a given wellbore. The wellbore and/or wellbore equipment, e.g. packers, used in a given application also can provide space constraints or routing constraints which limit the number of control lines. Furthermore, even in applications that would allow the addition of control lines, the additional lines tend to slow installation and increase the cost of installing equipment downhole.
Attempts have been made to reduce the number of hydraulic control lines necessary to carry out given well related procedures. For example, multiplexers have been used to limit the number of hydraulic control lines. However, multiplexing systems often rely on an ability to generate multiple levels of pressure that are interpreted downhole. In some custom designed systems, the maximum number of well tools is limited to a number equal to the number of hydraulic control lines. In other attempts, electric/solenoid controlled valves or custom hydraulic devices and tools have been designed to respond to pressure pulse sequences delivered downhole. However, many such systems have proved to be fairly costly and relatively slow to actuate.